It has been known in the past to combine polymers into interpenetrating networks in order to gain useful properties from the combination of materials. An interpenetrating network is a combination of two polymers in network form, at least one of which is synthesized and/or cross-linked in the immediate presence of the other. In the last several years, much work has been done on interpenetrating network systems (see L.H. Sperling, Interpenetrating Polymer Networs and Related Materials, Plenum Press, 1981; D. Klempner and K. C. Frisch, eds., "Polymer Networks", Polymer Science and Technology, Vol. 10, 1980; Y. S. Lipatov and L. M. Sergeeva, Interpenetrating Polymeric Networks, Naukova Dumka, Kiev, 1979; etc., for reviews). If one of the polymers is linear and one is crosslinked, a semi-interpenetrating polymer network (semi-IPN) results. A semi-IPN can be further categorized. If the first-formed system is crosslinked and the second is linear, it is a semi-1-IPN. The reverse situation yields a semi-2-IPN.
Semi-interpenetrating networks made to date have combined polymers that have different repeating units. An example of such an interpenetrating network is found in U.S. Pat. No. 4,302,553 (Frisch et al.) which discloses macrocylic structures of chemically different cross-linking polymers entangled with each other. Other semi-IPNs made previously have combined a linear and cross-linked polymer with different functional groups, e.g., a polymethylmethacrylate and a polyurethane. No one has yet combined two polymers which have identical recurring units into an interpenetrating network. The combination of a linear polymer and a cross-linkable oligomer with identical repeating units would give a semi-interpenetrating network of improved characteristics.